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<title>C Implementation (Using the GNU Compiler Collection (GCC))</title>

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<div class="chapter-level-extent" id="C-Implementation">
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Next: <a href="C_002b_002b-Implementation.html" accesskey="n" rel="next">C++ Implementation-Defined Behavior</a>, Previous: <a href="Invoking-GCC.html" accesskey="p" rel="prev">GCC Command Options</a>, Up: <a href="index.html" accesskey="u" rel="up">Introduction</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html" title="Index" rel="index">Index</a>]</p>
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<h2 class="chapter" id="C-Implementation_002dDefined-Behavior"><span>4 C Implementation-Defined Behavior<a class="copiable-link" href="#C-Implementation_002dDefined-Behavior"> &para;</a></span></h2>
<a class="index-entry-id" id="index-implementation_002ddefined-behavior_002c-C-language"></a>

<p>A conforming implementation of ISO C is required to document its
choice of behavior in each of the areas that are designated
&ldquo;implementation defined&rdquo;.  The following lists all such areas,
along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC
9899:1999 and ISO/IEC 9899:2011 standards.  Some areas are only
implementation-defined in one version of the standard.
</p>
<p>Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as &ldquo;determined by ABI&rdquo; below.  See <a class="xref" href="Compatibility.html">Binary
Compatibility</a>, and <a class="uref" href="https://gcc.gnu.org/readings.html">https://gcc.gnu.org/readings.html</a>.  Some
choices are documented in the preprocessor manual.
See <a data-manual="cpp" href="https://gcc.gnu.org/onlinedocs/cpp/Implementation_002ddefined-behavior.html#Implementation_002ddefined-behavior">Implementation-defined
behavior</a> in <cite class="cite">The C Preprocessor</cite>.  Some choices are made by the
library and operating system (or other environment when compiling for
a freestanding environment); refer to their documentation for details.
</p>

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<li><a href="Translation-implementation.html" accesskey="1">Translation</a></li>
<li><a href="Environment-implementation.html" accesskey="2">Environment</a></li>
<li><a href="Identifiers-implementation.html" accesskey="3">Identifiers</a></li>
<li><a href="Characters-implementation.html" accesskey="4">Characters</a></li>
<li><a href="Integers-implementation.html" accesskey="5">Integers</a></li>
<li><a href="Floating-point-implementation.html" accesskey="6">Floating Point</a></li>
<li><a href="Arrays-and-pointers-implementation.html" accesskey="7">Arrays and Pointers</a></li>
<li><a href="Hints-implementation.html" accesskey="8">Hints</a></li>
<li><a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html" accesskey="9">Structures, Unions, Enumerations, and Bit-Fields</a></li>
<li><a href="Qualifiers-implementation.html">Qualifiers</a></li>
<li><a href="Declarators-implementation.html">Declarators</a></li>
<li><a href="Statements-implementation.html">Statements</a></li>
<li><a href="Preprocessing-directives-implementation.html">Preprocessing Directives</a></li>
<li><a href="Library-functions-implementation.html">Library Functions</a></li>
<li><a href="Architecture-implementation.html">Architecture</a></li>
<li><a href="Locale_002dspecific-behavior-implementation.html">Locale-Specific Behavior</a></li>
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